This invention relates, in general terms, to an improved form of lift or elevator system, and to parts of and components therefor. More particularly, but not exclusively, the invention relates to a lift or elevator system, and an overall drive means therefor, which is responsible for a substantial saving in power input and energy use, and accordingly cost, when compared with the known art. The invention also relates to a multi-stage hydraulic cylinder system which is especially suited for use in lift or elevator systems of the aforementioned type, but is adaptable for use in other contexts.
Throughout the ensuing description, for ease of explanation reference will be made to a so-called hydraulic lift. It must be realised, however, that the present invention is not to be considered to be restricted solely to such types of lifts and in fact in certain aspects of the present invention need not even be restricted to the field of lifts. More especially, the present invention will be equally suitable for use with:
(1) traction elevators; PA1 (2) hydraulic elevators wherein motion is achieved through the operation of a ram or cylinder; and PA1 (3) any drive system that uses hydraulic fluid under pressure. PA1 (1) electrical traction drives; PA1 (2) a combination of electrical means and screw drives; and PA1 (3) hydraulic cylinder-ram drives.
Hydraulic lifts as currently in use employ a pump and a drive means or motor to deliver oil under pressure to a cylinder and associated piston, thereby giving rise to linear motion as a result of extension of the cylinder. Such linear motion, initially in a vertical direction, allows for movement of a lift car or carriage between prearranged storeys or levels of any given structure. Of course once the lift car or carriage is moved upwardly, it ultimately becomes necessary to allow for movement downwardly. In accordance with the known art the majority of lifts are made to move in a downwards direction by the utilization of appropriate valving for venting of the oil or other hydraulic fluid, which is under pressure, back to a storage tank for such fluid, which is generally speaking at atmospheric pressure. In practical terms it should therefore be realised that power or energy is necessary in order to actuate or operate such a hydraulic system whereby to allow for upward movement of the lift or carriage. Such hydraulic fluid under pressure is a source of potential energy, in practical terms representing a reservoir of stored energy. Unfortunately, however, in accordance with known apparatus practices and techniques, such stored energy is, to all intents and purposes, totally dissipated and lost as a result of venting of the oil to atmosphere on what might be termed the down stroke. Put simplistically, therefore, hydraulic lift systems of this known type require energy input to produce vertical upward movement but then rely in effect on gravity to produce subsequent downward movement. In terms of moving a dead weight between vertical storeys of a building or the like structure, the energy or power input necessary therefore can be quite substantial. Furthermore, large electric motors are invariably needed, since the car is not counterweighted, and this requires substantial electrical wiring. As such, because of the power input needed, the plant required in accordance with the known art has been bulky, space-consuming and expensive.
Again in accordance with the known art, lift or elevator systems currently in use for the transport of passengers or plant between spaced-apart levels utilise or employ three basic methods or means of achieving the desired motion and control thereof. These three methods are:
The hydraulic ram configuration generally includes a single or multiple-element piston in an appropriate housing, with the piston itself moving in direct proportion to input flow and having a stroke length somewhat less than the retracted length. In accordance with known techniques such a hydraulic ram can be mounted either underneath the lift car or carriage, or alternatively along-side that car or carriage, dependent upon the amount of space available. One disadvantage associated with a configuration wherein the ram is mounted underneath he car or carriage resides in the need for the provision of a caisson, with no such caisson actually being required in an arrangement utilising a ram mounted along-side the car or carriage.
When the required length of travel for the lift or elevator is longer than the maximum available retracted length of the ram, as is quite often the case, then in accordance with the known techniques it has become necessary to rely on a compound and complicated design or configuration termed "a phasing telescopic cylinder" and involving a sleeving assembly. Such a configuration utilises telescopic or telescoping rods, one inside the other, of a suitable number whereby to bring about the desired length of travel for the overall lift car or carriage. In a practical sense, however, in order to achieve constant car speed, avoiding jerky motion, each rod or tube must be what is termed "phased". In other words, each sleeve must be adapted to move at the same time. In hydraulic terms such can be achieved by feeding the annulus fluid from each rod section to the full cross-sectional area of the next inner cylinder. The diameter is calculated in order to achieve constant relative speeds between adjacent tubes. Other methods, such as for example phasing by connecting each stage through a series of chains or slings, could also be used. Again in practical terms, in order to bring about constant speed and smooth travel of lift or car, all tubes must reach the end of their stroke together.
With such arrangements rephasing checks are required in each tube section. In practical terms such configurations have been found to work relatively satisfactorily. By the same token, however, such prior art arrangements have been determined to suffer from several important advantages. First of all, the rather complicated telescoping cylinder arrangement is difficult and accordingly expensive to manufacture. Secondly, such a configuration requires in effect two distinct sealing areas for each telescoping or telescopic section. Thirdly, such a configuration has been found to be inordinately bulky. Fourthly, such a configuration has been found to require special machinery to manufacture. All these factors give rise to their own problems, and the end result is an overall arrangement which, apart from being rather complicated in operation, is expensive in manufacture, installation and maintenance. Such expensive configurations have resulted in a limitation on the exploitation of such an arrangement.